Method of detecting relative position of exposure mask and object to be exposed, alignment method, and exposure method using the same

ABSTRACT

An alignment method for an exposure mask and an object to be exposed, wherein exposure is carried out while the exposure mask having a light blocking film formed at a membrane portion thereof is closely contacted to the object to be exposed and light from a light source is projected to the object to be exposed, through the exposure mask, and wherein alignment of the exposure mask and the object to be exposed is carried out prior to the exposure, the method comprising the steps of preparing an exposure mask having a light blocking film provided on a base material constituting the membrane portion and having a structure for performing position detection, flexing the membrane portion and detecting, by use of the structure, a relative position of the exposure mask and the object to be exposed, in a state in which the exposure mask is contacted to the object to be exposed, and aligning the exposure mask and the object to be exposed, with each other, on the basis of a result of the position detection.

TECHNICAL FIELD

This invention relates to exposure technology that enables manufactureof fine patterns and, specifically, to a method of detecting a relativeposition of an exposure mask and an object to be exposed, an alignmentmethod, an exposure method using such alignment method, an exposuremask, and an exposure apparatus having such mask.

BACKGROUND ART

Because of continuing increases in capacity of a semiconductor memory orin speed or integration density of a CPU processor, further advancementsof microprocess based on optical lithography are indispensable.

Generally, the limit of microprocess using optical lithographyapparatuses is of an order of the wavelength of used light. For thisreason, the wavelengths of light used in optical lithographicapparatuses have been shortened. Currently, near-ultraviolet ray lasersare used, and the microprocessing of 0.1 micron order is enabled.

Although the minuteness attainable with the optical lithography hasadvanced, in order to accomplish microprocessing of an order of 0.1micron or narrower, there still remain many problems to be solved, suchas the necessity of shortening the laser wavelength further, ordeveloping lenses usable with such wavelength region.

On the other hand, as a measure for enabling optical microprocessing ofan order of 0.1 micron or narrower, a microprocessing apparatus using astructure of near-field optical microscope, hereinafter “SNOM” (ScanningNear-field Optical Microscope), has been proposed. An example is anapparatus in which, by use of evanescent light seeping or escaping fromsmall openings of a size not greater than 100 nm, local exposureexceeding the limit of the wavelength of light is carried out to aresist.

However, in lithographic apparatuses using such SNOM structure, themicroprocessing is carried out on the basis of continuous drawing usingone probe (or a few probes). Thus, there is a problem of low throughput.

As a measure for solving this problem, U.S. Pat. No. 6,171,730 disclosesa method in which a photomask is formed with a pattern designed so thatnear-field seeps from between light blocking films and the exposure iscarried out while the photomask is closely contacted to a photoresistapplied to a substrate, so that a fine pattern of the photomask istransferred to the resist at once.

The method and apparatus disclosed in the specification of this patentis excellent, and it makes a large contribution to the technical fieldto which the present invention belongs.

The near-field exposure method can produce a fine pattern of an order oftens nanometers, being much smaller than the wavelength of light usedfor the exposure. For this reason, in the aforementioned U.S. patent,the photomask is provided with a membrane portion and, by flexing it,the membrane portion is approximated to a photoresist up to thenear-field region, such that the exposure is carried out in intimatecontact state.

Here, if the alignment operation is carried out while the membraneportion of the photomask and the photoresist are spaced from each otherand if they are subsequently approximated to each other up to thenear-field region and the exposure is carried out in such state, it maycause a positional deviation of the near-field exposure pattern, due tothe flexure of the membrane portion. Also, such positional deviation maycause a decrease of the yield of device production.

However, conventional reduction projection system optical lithography oralignment methods for X-ray exposure using a mask having a membraneportion are basically an exposure method in which, during the exposureprocess, the photoresist and the photomask are exposed while they arekept separated from each other. Thus, in these methods, there is nosuggestion for a problem in a case in which, during the exposureprocess, a photomask and a photoresist are exposed while they are placedclose to or in intimate contact with each other. Therefore, theseconventional methods can not be directly applied to an alignment methodfor the near-field exposure.

On the other hand, U.S. Pat. No. 6,252,649 discloses an alignercomprising: an aligner device for relatively moving and aligning a maskhaving a pattern depicted thereon to be exposed and an object having aphotosensitive layer to be subject to the exposure through said mask; acontacting device for contacting said mask and said object as aligned; adetecting device for detecting the alignment accuracy of said mask andsaid object as contacted; separating means responsive to said detectingdevice for separating said mask and said object from each other when thealignment accuracy of said contacted mask and object is detected by saiddetecting device to be out of a predetermined tolerance and in order toalign said mask and said object again; and an exposure apparatus forexposing said mask to said object as contacted with each other.

Additionally, the aforementioned U.S. Pat. No. 6,252,649 shows aspecific aligner in which a pressure film is used to press a film-maskthereby to cause deformation of the film-mask. The pressure film isexpanded to press the film-mask against the work to closely contact theformer to the latter.

However, in the aligner apparatus disclosed in U.S. Pat. No. 6,252,649,the pressure film and the film-mask are made separate such that there isa space between the pressure film and the film-mask. Thus, if a foreignparticle such as dust is present in such space, it may cause incompletecontact of the mask to the workpiece. Even if the close contact iscomplete, the light projected from a light source would be influenced bythe foreign particle, and accurate exposure would be prevented thereby.

DISCLOSURE OF THE INVENTION

The present invention provides a method and an apparatus by which theabove-described problems can be solved.

The present invention provides a method of detecting a relative positionof an exposure mask and an object to be exposed, wherein exposure iscarried out while the exposure mask having a light blocking film formedat a membrane portion thereof is closely contacted to the object to beexposed and light from a light source is projected to the object to beexposed, through the exposure mask, and wherein the relative position ofthe exposure mask and the object to be exposed is to be detected priorto the exposure, characterized by the steps of: preparing the exposuremask having a light blocking film provided on a base materialconstituting the membrane portion and having a structure for performingposition detection; and flexing the membrane portion and detecting, byuse of the structure, a relative position of the exposure mask and theobject to be exposed, in a state in which the exposure mask is contactedto the object to be exposed.

The present invention provides an alignment method for an exposure maskand an object to be exposed, wherein exposure is carried out while theexposure mask having a light blocking film formed at a membrane portionthereof is closely contacted to the object to be exposed and light froma light source is projected to the object to be exposed, through theexposure mask, and wherein alignment of the exposure mask and the objectto be exposed is to be carried out prior to the exposure, characterizedby the steps of: preparing the exposure mask having a light blockingfilm provided on a base material constituting the membrane portion andhaving a structure for performing position detection; flexing themembrane portion and detecting, by use of the structure, a relativeposition of the exposure mask and the object to be exposed, in a statein which the exposure mask is contacted to the object to be exposed; andaligning the exposure mask and the object to be exposed, with eachother, on the basis of a result of said position detection.

In accordance with the present invention, where a deviation withreference to a position to be exposed is detected by said positiondetection, the flexure of the membrane portion may be removed and theexposure mask and the object to be exposed may be relatively moved so asto remove the positional deviation, and subsequently, the membraneportion may be flexed again to be contacted to the object to be exposedand, in that state, the position detection may be carried out, whereinthe above-described procedure may be repeated once or more until thedeviation comes into a predetermined tolerable range for exposureprecision, whereby the alignment is carried out.

In accordance with the present invention, the structure for performingthe position detection may be formed adjacent a center of the membraneor around the membrane.

The present invention provides an exposure method, characterized by thesteps of: aligning an exposure mask and an object to be exposed, by useof an alignment method of the present invention; and performing exposureby projecting light from a light source to the object to be exposed,through the exposure mask, while the exposure mask is closely contactedto the object to be exposed.

The present invention provides an exposure mask having a membraneportion including a flexible structure, characterized in that a lightblocking film is provided on a base material constituting the membraneportion, and that a structure for performing alignment of the object tobe exposed and the exposure mask is provided at a central portion of themembrane portion or around the membrane portion.

In the exposure mask according to the present invention, the structurefor performing the alignment may be constituted by an opening formed insaid light blocking film.

The present invention provides an exposure apparatus, characterized by:an exposure mask of the present invention; a pressure adjusting devicefor causing flexure of a membrane portion of the mask; a first drivingdevice for narrowing a distance between the mask and a workpiece havingan object to be exposed, applied thereto; a second driving device forestablishing parallelism between a mask surface of the mask and asurface of the object to be exposed; a position detecting mechanism fordetecting a position to be exposed, by use of a structure for performingthe alignment; a third driving device for changing a relative positionof the mask and the workpiece having the object to be exposed, on thebasis of information supplied from said position detecting mechanism;and an exposure light source.

In accordance with the present invention, when an exposure mask having amembrane portion is closely contacted to a photoresist and exposure iscarried out, the position can be detected with smaller deviation withrespect to the position to be detected. Thus, the present inventionassures an alignment method, an exposure method using the alignmentmethod, an exposure mask, and an exposure apparatus having such mask, bywhich the yield of device production can be improved.

Particularly, in the present invention, the mask is provided with alight blocking film formed on a base material constituting the membraneportion. Thus, the light blocking film and the membrane portion areformed integrally. Therefore, there is no possibility of dust or anyother foreign particles entering between them, and the above-describedtechnical advantages are still assured.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plane view of a photomask in an embodiment of the presentinvention, as seen from the entrance side of exposure light.

FIGS. 2A and 2B are sectional views, taken on line A-A′, of thephotomask in an embodiment of the present invention shown in FIG. 1.

FIGS. 3A-3D are views for explaining the procedure of near-fieldexposure method using a photomask of the structure shown in FIG. 2A, inan embodiment of the present invention.

FIGS. 4A-4D are views for explaining the procedure of exposure method inan embodiment of the present invention, in a case where breakage of amembrane, for example, is a problem to be considered.

FIGS. 5A-5D are views for explaining the procedure of exposure method inan embodiment of the present invention, in a case where a structure tobe used for the alignment is formed around the membrane.

FIG. 6 is a sectional view of a photomask and a workpiece to beprocessed, in Example 1 of the present invention.

FIGS. 7A-7E are views for explaining the procedure optical nano-imprintexposure method using a membrane mask in Example 3 of the presentinvention.

BEST MODE FOR PRACTICING THE INVENTION

FIG. 1 is a plane view of a photomask in an embodiment of the presentinvention, as seen from the entrance side of exposure light.

In FIG. 1, the photomask comprises a photomask support 100, a membraneportion 101 having a thickness of about 0.1-100 μm, and an opening 102to be used in first-stage alignment. Additionally, while not shown inFIG. 1, the photomask further comprises a membrane base material 103, alight blocking film 104, an exposure pattern 105 formed at the back sideof the membrane portion, and a structure 106 to be used in second-stagealignment.

Here, the opening 102 to be used for the first-stage alignment isnecessary only when the first-stage alignment is to be performed. Anexample is the exposure of a workpiece for producing a structure in afirst layer. If strict positional precision is not required for theworkpiece, the first-stage alignment may be omitted. In such case, as amatter of course, the opening for use in the first-stage alignment isunnecessary.

FIG. 1 shows a case where there are four membrane portions 101. However,a single photomask may have membrane portions of any number. From thestandpoint of strength of the photomask, the membrane portions maypreferably be disposed symmetrically with respect to the center of thephotomask.

As regards the shape of the membrane, although a square shape isillustrated, it may have any other shape. From easiness of process, anoblong shape is good, but where tensile stress or distortion of themembrane as it is flexed are taken into account, the square shape ispreferable than the oblong shape. Also, while the easiness of processmay be inferior, a regular polygon having vertices of a number largerthan that of the square shape is preferable.

Although the photomask support 100 illustrated has a rectangular shape,it may have any other shape, such as a circular shape, for example. Fromthe standpoint of performing initial alignment prior to the first-stagealignment, a rectangular or even a circular shape with an orientationflat is preferable, because the orientation can be detected easily.

As regards the opening 102 to be used for the first-stage alignment, theillustrated example uses two cross-shaped openings. Thepresence/absence, disposition, number and shape of the openings may bedifferent in accordance with the necessity of the first-stage alignmentand the required precision thereof.

FIG. 2 shows the section, along a line A-A′, of the photomask shown inFIG. 1. In FIG. 2, denoted at C is the center of the photomask. Also,FIG. 2 illustrates an opening defined by processing the light blockingfilm 104, as an example of the structure 106 to be used in thesecond-stage alignment.

As regards the alignment method for the second stage, various methodsare usable such as, for example, a method in which light of lowsensitivity to the workpiece is projected through use of an opening andthe quantity of reflected light from the structure formed on theworkpiece is detected, or an image is provided by reflected light.Alternatively, the quantity or intensity of light emission from afluorescent substance provided on the workpiece may be detected.

As regards the structure for use in the alignment, in place of theopening, an STM (scanning tunnel microscope) probe structure may be usedand, in that occasion, the shape of a structure formed on the workpiececan be detected.

The exposure pattern 105 shown in FIG. 2 is merely an example. Thispattern is variable arbitrarily in accordance with what is required forthe product. Specifically, FIG. 2A shows a case wherein the structure106 to be used for the second-stage alignment is formed adjacent thecenter of the membrane portion 101. FIG. 2B shows a case wherein thestructure 106 is formed around the membrane portion 101.

Referring to FIG. 3, the near-field exposure method using a photomask ofthe structure shown in FIG. 2A, will be explained.

First of all, the photomask having a structure to be used in thesecond-stage alignment, formed adjacent the center of the membraneportion 101, is disposed so that its light blocking film is opposed to aphotoresist 300 formed on the workpiece 301, the photoresist being theobject to be exposed (FIG. 3A). Here, as regards the distance betweenthe light blocking film surface and the photoresist surface, although itdepends on the area of the membrane portion, from the standpoint of thedurability of the membrane portion, the distance should be not greaterthan 100 μm and they should be placed close to each other unless themembrane portion and the photoresist surface do not contact with eachother.

Subsequently, by decreasing the pressure between the membrane portion101 and the photoresist 300 or, alternatively, by pressurizing themembrane 101 from the mask support 100 side, the membrane 101 is flexeduntil only the central portion thereof contacts the photoresist 300(FIG. 3B).

Then, position detection is carried out by using the structure 106(alignment marker) to be used in the second-stage alignment formedadjacent the center of the membrane portion 101 as well as an alignmentmarker structure provided on the workpiece 301. If a deviation betweenthis position and the position to be exposed is within a tolerable rangefor the required exposure precision, the photomask is further flexed sothat the whole surface of the exposure pattern is closely contacted tothe photoresist 300. Thereafter, the exposure is carried out.

If the deviation is beyond the tolerable range for the required exposureprecision, the relative position of the photomask and the workpiece isshifted in a direction of an arrow, being parallel to the opposedsurfaces of them, while the central portion of the membrane and thephotoresist are kept in contact with each other, and they are broughtinto alignment with each other so that the positional deviation comesinto the tolerable range (FIG. 3C).

After this, the photomask is flexed furthermore and the whole surface ofthe exposure pattern is closely contacted to the photoresist. Then,exposure light is projected to the membrane from the photomask supportside, and exposure is carried out (FIG. 3D).

With this arrangement, the exposure can be accomplished while thepositional deviation between prior to flexing the membrane portion andat the time of exposure where the membrane is flexed is removed.Therefore, the positional deviation of the pattern can be made small,and the yield of device production can be improved.

Where relatively moving the central portion of the membrane and thephotoresist while they are kept in contact with each other may cause aproblem such as breakage of the membrane, shortening the lifetime of themembrane, roughing the photoresist surface (it may cause a problem in apost-process), for example, the procedure shown in FIG. 4 may be used.

What differs from the above-described procedure is as follows. Theposition detection is carried out by using structures (alignment markerstructures) for use in the second-stage alignment, provided on theworkpiece 301 and the membrane portion 101. If the deviation betweenthis position and the position to be exposed is out of the tolerablerange for the required exposure precision, first the flexure of themembrane portion is removed to separate the membrane and the photoresistfrom each other. After this, the relative position of the photomask andthe workpiece is moved in a direction of an arrow, being parallel to theopposed surfaces of them, so that they are brought into alignment (FIG.4C).

Subsequently, the membrane portion is flexed again to the extent thatonly the central portion of the membrane contacts the photoresist, andthen the position detection is carried out. If a deviation between thisposition and the position to be exposed is within a tolerable range forthe required exposure precision, the photomask is further flexed so thatthe whole surface of the exposure pattern is closely contacted to thephotoresist 300. Thereafter, the exposure is carried out (FIG. 4D).

If the deviation is beyond the tolerable range for the required exposureprecision, even after completion of the translational motion (FIG. 4C),the above-described procedure, that is, the operation of FIGS. 4B and4C, is repeated.

If the deviation between this position and the position to be exposedcomes into a tolerable range for the required exposure precision, thephotomask is further flexed so that the whole surface of the exposurepattern is closely contacted to the photoresist 300. Thereafter, byprojecting exposure light to the membrane from the mask support side,the exposure is carried out (FIG. 4D).

With this arrangement, the exposure can be accomplished while thepositional deviation between prior to flexing the membrane portion andat the time of exposure where the membrane is flexed is removed.Therefore, the positional deviation of the pattern can be made small,and the yield of device production can be improved.

Furthermore, since a force to be applied to the central portion of themembrane or to a photoresist that contacts to the central portion of themembrane is reduced, the lifetime of the photomask can be prolonged anddeterioration of the resist pattern can be prevented.

If the structure (alignment marker structure) to be used in thesecond-stage alignment can not be formed adjacent the membrane center,for some reason related to the exposure pattern, such structure may beprovided around the membrane as in the photomask shown in FIG. 2B.

Referring to FIG. 5, the near-field exposure method using a photomask ofthe structure shown in FIG. 2B, will be explained.

First of all, a photomask having a structure 106 (alignment markerstructure) to be used in the second-stage alignment, formed around themembrane portion 101, is disposed so that, like the example of FIG. 3,its light blocking film is opposed to a photoresist 300 formed on theworkpiece 301, the photoresist being the object to be exposed (FIG. 5A).

Subsequently, the membrane portion 101 is flexed until the portionhaving the structure 106 is contacted to the photoresist 300 (FIG. 5B).

Then, position detection is carried out by using the structure(alignment marker structure), to be used in the second-stage alignment,provided on the membrane portion 101 and the workpiece 301. If adeviation between this position and the position to be exposed is withina tolerable range for the required exposure precision, the photomask isfurther flexed so that the whole surface of the exposure pattern isclosely contacted to the photoresist 300. Thereafter, the exposure iscarried out.

Here, a plurality of alignment marker structures for use in thealignment may be provided at symmetrical positions about the membranecenter, and in that occasion, the positional deviation can be detectedfrom an average of the positions detected by these structures. Thisimproves the precision much more, and it is particularly effective tothe correction of positional deviation caused as a result of flexing themembrane.

If the deviation is beyond the tolerable range for the required exposureprecision, the relative position of the photomask and the workpiece isshifted in a direction of an arrow, being parallel to the opposedsurfaces of them, and they are brought into alignment with each other sothat the positional deviation comes into the tolerable range. Afterthis, the photomask is flexed furthermore and the whole surface of theexposure pattern is closely contacted to the photoresist 300. Then,exposure light is projected to the membrane from the photomask supportside, and exposure is carried out (although not shown in the drawings).

If relatively moving the central portion of the membrane and thephotoresist while they are kept in contact with each other may cause aproblem such as breakage of the membrane, reduction in lifetime of themembrane, roughing of the photoresist surface (resulting in a problem ina post-process), for example, the flexure of the membrane portion may beremoved and, after this, the relative position of the photomask and theworkpiece may be moved in parallel to the opposed surfaces of them (FIG.5C).

If the deviation is beyond the tolerable range for the required exposureprecision, even after completion of the translational motion, theabove-described procedure is repeated until the deviation comes withinthe tolerable range for the required exposure precision, like the caseof FIG. 4 (FIG. 5D).

With this arrangement, even if the structure to be used in thesecond-stage alignment can not be formed adjacent the membrane center,for some reason related to the exposure pattern, the exposure can beaccomplished while the positional deviation between prior to flexing themembrane portion and at the time of exposure where the membrane isflexed is removed. Therefore, the positional deviation of the patterncan be made small, and the yield of device production can be improved.

Furthermore, when the relative position of the photomask and theworkpiece is to be changed, the flexure of the membrane portion isremoved and the membrane is separated from the photoresist. As a result,a force to be applied to the central portion of the membrane or to aphotoresist that contacts to the central portion of the membrane isreduced. Therefore, the lifetime of the photomask can be prolonged anddeterioration of the resist pattern can be prevented.

In an alignment method according to the present invention, if theperipheral portion of the membrane mask is supported by a rigidsupporting member such as shown in FIG. 1, deformation of the membraneresponsive to pressure application is such that the membrane centershifts in a direction of a normal to the membrane surface. Suchdeformation is similar to deformation of a beam being supported at itsopposite ends, and it shows excellent parallelism in the normaldirection as well as a good reproducibility. Thus, it provides anadvantage of higher precision alignment.

Regarding the alignment method, while the near-field exposure method hasbeen explained as an example, the present invention is not limited tothis. The present invention is applicable also to any other exposuremethod such as, for example, an optical nano-imprint exposure method inwhich a membrane mask is flexed.

Next, some examples of the present invention will be explained.

EXAMPLE 1

FIG. 6 is a schematic view of a portion of a photomask and a workpieceused in this example.

As regards the photomask support, Si substrate 600 was used. On this Sisubstrate 600, SiN film 601 as membrane base material was formed with afilm thickness of 300 nm. On this film, Cr film 602 which functions as alight blocking film for the exposure light was formed by vapordeposition, with a film thickness of 50 nm. By processing the Cr film602 by use of an FIB (focusing ion beam) processing machine, an exposurepattern 105 (an original pattern for exposure of the photoresist) and anopening 605 to be used in the second-stage alignment were produced in aportion of the Cr film 602. The exposure pattern 105 includes a finepattern having a smallest linewidth of 50 nm.

Thereafter, back-etching of the Si substrate 600 was carried outrelative to the SiN film 601, from the side of the photomask remote fromits Cr film 602 portion, whereby the membrane portion 101 was formed.During the back-etching of the Si substrate 600, the openings (notshown) to be used in the first-stage alignment were also made.

In this example, in regard to a Si pattern 606 formed upon an insulativefilm 607 on a Si substrate 608, SOI substrate having a fine metalpattern formed thereon was used as a workpiece substrate. On thisworkpiece substrate, a lower-layer thick resist 604 was formed by spincoating, with a film thickness 200 nm. Then, it was heated in an oven at200° C. for one hour. Thereafter, a Si containing resist 603 for g-lineexposure was applied to a film thickness of 50 nm, and pre-baking wasperformed by using a hot plate, at 90° C. for 90 seconds.

The Cr film side (light blocking film) of the photomask and the Sicontaining resist 603 side of the SOI substrate were disposed opposed toeach other. The photomask was held by fixing the Si substrate 600(supporting portion) by use of a vacuum chuck. Regarding the SOIsubstrate, the Si substrate 608 was fixed on a stage. In such state, thelight blocking film surface (Cr film 602) and the Si containing resist603 surface were approximated to each other so that the interval betweenthem became equal to 50 μm.

In such state, the opening to be used in the first-stage alignment wasused, and yellow light provided by cutting short wavelengths in whitelight, having high exposure sensitivity to the Si containing resist, wasused to perform the alignment, whereby rough alignment of the photomaskand the workpiece opposed to it was carried out.

Subsequently, a pump was used to pressurize the membrane portion 101from the Si substrate 600 side, to cause flexure of the membrane portion101. Simultaneously, similar yellow light as described above was used,and while observing interference fringe produced on the membrane fromthe photomask supporting member side, only the Cr film adjacent theopening 605 was brought into contact with the Si containing resist 603.In such state, through the opening 605 formed adjacent the center of themembrane portion 101, light of a wavelength having low exposuresensitivity to the Si containing photoresist 603 was projected, and theintensity of reflected light from the Si pattern 606 was detected by adetector. Based on this, a relative positional deviation between thephotomask and the workpiece is detected. Since this example used Sicontaining resist for g-line exposure light, a red laser of a wavelength635 nm was used to perform the position detection, and a positionaldeviation of 0.7 μm was found with respect to the alignment marker onthe SOI substrate.

The positional deviation was removed by moving a stage on the SOIsubstrate side, and thereafter, by pressuring the membrane until thewhole surface of the exposure pattern in the membrane closely contactedto the Si containing resist 603, whereby the membrane 101 was flexed. Insuch state, light from an Hg lamp was projected to the whole surface ofthe photomask from the Si substrate 600 side, whereby the exposure wascarried out.

Subsequently, by developing the Si containing resist 603, a pattern ofthe Si containing resist 603 was produced. By using it as a mask and byusing an oxygen gas, dry etching was carried out to the lower-layerthick resist 604, whereby a resist pattern was produced. Thereafter,metal was applied by vapor deposition and, then, the resist was removed.With this procedure, a fine metal pattern having a small positionaldeviation with respect to the Si pattern 606 on the insulating film 607can be produced. Therefore, the yield of device production can beimproved.

EXAMPLE 2

In this embodiment, the procedure up to the position detection using theopening 605 is the same as Example 1, and description thereof will beomitted.

Like Example 1 described above, position detection was carried out byuse of red laser of a wavelength 635 nm, and it was found a positionaldeviation of 0.7 μm with respect to an alignment marker on the SOIsubstrate.

Here, by using a pump, the membrane portion 101 was depressurized fromthe Si substrate 600 side to reduce the flexure of the membrane portion101, so that the membrane portion 101 was disengaged from the Sicontaining resist 603. Also, it can be checked by observing interferencefringe produced at the membrane, by use of yellow light and from thephotomask supporting member side.

Thereafter, the stage at the SOI substrate side was moved to remove thepositional deviation, and then the membrane was pressurized until thewhole surface of the exposure pattern of the membrane was closelycontacted to the Si containing resist 603, whereby the membrane portion101 was flexed. In such state, light from an Hg lamp was projected tothe whole surface of the photomask from the Si substrate 600 side, andexposure was carried out. The procedure following this is similar tothat of Example 1.

With the exposure process according to the method described above, afine metal pattern having a small positional deviation with respect tothe Si pattern 606 on the insulating film 607 was produced. Further, themembrane breakage frequency was reduced and the pattern shape of the Sicontaining resist after the development was improved. Thus, the yield ofdevice production was improved significantly.

EXAMPLE 3

Referring to FIG. 7, an example wherein the present invention is appliedto an optical nano-imprint exposure method in which a membrane mask isflexed, will be described.

As shown in FIG. 7A, a mask is constituted by a membrane 701 of athickness of 0.1-100 μm, and it has an irregularity (inequality)structure 702 formed at its front face. The alignment method in suchoptical nano-imprint exposure method using such mask will be performedin the following manner.

First of all, a membrane mask having a mask side marker structure 705,to be used in fine alignment to be performed after rough alignment,formed adjacent the center of the membrane 701, is disposed so that itsfront face is opposed to an ultraviolet-ray setting resin liquid 704(object to be exposed) provided on a workpiece 703 (FIG. 7A).

Subsequently, by depressurizing the space between the membrane 701portion and the ultraviolet-ray setting resin liquid 704 or bypressurizing the membrane 701 portion from the back side of the membranemask supporting member 706, the membrane 701 portion is brought intocontact, from its central portion, with the ultraviolet-ray settingresin liquid 704. Thus, the membrane is flexed so that the inequalitystructure 702 at the membrane mask surface sink into the ultraviolet-raysetting resin liquid 704 (FIG. 7B).

Then, position detection is carried out by using a mask-side markerstructure 705 to be used in the fine alignment, formed adjacent thecenter of the membrane 701 portion as well as a substrate-side markerstructure 707. If a deviation between this position and the position tobe exposed is within a tolerable range for the required exposureprecision, (as will be described with reference to FIGS. 7D and 7E) themembrane mask is further flexed so that the whole surface of theinequality structure pattern 702 sinks into and is intimately contactedto the ultraviolet-ray setting resin liquid 704, till a portion adjacentthe surface of the workpiece 703. Thereafter, ultraviolet light isprojected to set the resin liquid 704.

If the deviation is beyond the tolerable range for the required exposureprecision, the relative position of the membrane mask 701 and theworkpiece 703 is shifted in a direction of an arrow, being parallel tothe opposed surfaces of them, while the central portion of the membrane701 and the ultraviolet-ray setting resin liquid 704 are kept in contactwith each other, and thus alignment is carried out (FIG. 7C).

After this, the membrane mask is flexed furthermore and the wholesurface of the inequality structure 702 pattern is sank into theultraviolet-ray setting resin liquid 704, up to a portion adjacent thesurface of the workpiece 703 (FIG. 7D). Thereafter, the ultravioletlight is projected to set the resin liquid 704 (FIG. 7E).

With this arrangement, the exposure can be accomplished while thepositional deviation between prior to flexing the membrane portion andat the time of exposure where the membrane is flexed is removed.Therefore, the positional deviation of the pattern can be made small,and the yield of device production can be improved.

1. In a method of detecting a relative position of an exposure mask andan object to be exposed, wherein exposure is carried out while theexposure mask having a light blocking film formed at a membrane portionthereof is closely contacted to the object to be exposed and light froma light source is projected to the object to be exposed, through theexposure mask, and wherein the relative position of the exposure maskand the object to be exposed is to be detected prior to the exposure,characterized by the steps of: preparing the exposure mask having alight blocking film provided on a base material constituting themembrane portion and having a structure for performing positiondetection; and flexing the membrane portion and detecting, by use of thestructure, a relative position of the exposure mask and the object to beexposed, in a state in which the exposure mask is contacted to theobject to be exposed.
 2. In an alignment method for an exposure mask andan object to be exposed, wherein exposure is carried out while theexposure mask having a light blocking film formed at a membrane portionthereof is closely contacted to the object to be exposed and light froma light source is projected to the object to be exposed, through theexposure mask, and wherein alignment of the exposure mask and the objectto be exposed is to be carried out prior to the exposure, characterizedby the steps of: preparing the exposure mask having a light blockingfilm provided on a base material constituting the membrane portion andhaving a structure for performing position detection; flexing themembrane portion and detecting, by use of the structure, a relativeposition of the exposure mask and the object to be exposed, in a statein which the exposure mask is contacted to the object to be exposed; andaligning the exposure mask and the object to be exposed, with eachother, on the basis of a result of said position detection.
 3. Analignment method according to claim 2, wherein, where a deviation withreference to a position to be exposed is detected by said positiondetection, the flexure of the membrane portion is removed and theexposure mask and the object to be exposed are relatively moved so as toremove the positional deviation, and subsequently, the membrane portionis flexed again to be contacted to the object to be exposed and, in thatstate, the position detection is carried out, and wherein theabove-described procedure is repeated once or more until the deviationcomes into a predetermined tolerable range for exposure precision,whereby the alignment is carried out.
 4. An alignment method accordingto claim 2, wherein the structure for performing the position detectionis formed adjacent a center of the membrane or around the membrane. 5.An exposure method, characterized by the steps of: aligning an exposuremask and an object to be exposed, by use of an alignment method asrecited in claim 2; and performing exposure by projecting light from alight source to the object to be exposed, through the exposure mask,while the exposure mask is closely contacted to the object to beexposed.
 6. An exposure mask having a membrane portion including aflexible structure, characterized in that a light blocking film isprovided on a base material constituting the membrane portion, and thata structure for performing alignment of the object to be exposed and theexposure mask is provided at a central portion of the membrane portionor around the membrane portion.
 7. An exposure mask according to claim6, wherein the structure for performing the alignment is constituted byan opening formed in said light blocking film.
 8. An exposure apparatus,characterized by: an exposure mask as recited in claim 6; a pressureadjusting device for causing flexure of a membrane portion of the mask;a first driving device for narrowing a distance between the mask and aworkpiece having an object to be exposed, applied thereto; a seconddriving device for establishing parallelism between a mask surface ofthe mask and a surface of the object to be exposed; a position detectingmechanism for detecting a position to be exposed, by use of a structurefor performing the alignment; a third driving device for changing arelative position of the mask and the workpiece having the object to beexposed, on the basis of information supplied from said positiondetecting mechanism; and an exposure light source.